feat(AppKit): add skill for Files plugin

[atilafassina]

this PR adds a skill to use the appKit files plugin to perform UC operations

Documentation safety checklist

• Examples use least-privilege permissions (no unnecessary ALL PRIVILEGES, admin tokens, or broad scopes)
• Elevated permissions are explicitly called out where required
• Sensitive values are obfuscated (placeholder workspace IDs, URLs, no real tokens)
• No insecure patterns introduced (e.g. disabled TLS verification, hardcoded credentials)

[Copilot]

Pull request overview

Adds AppKit documentation for using the files() plugin to perform Unity Catalog Volume operations, and wires the new reference into the Databricks Apps skill index/manifest.

Changes:

• Add a new AppKit reference page documenting UC Volume file operations via the files() plugin.
• Link the new Files guide from the Databricks Apps SKILL “Required Reading by Phase” table.
• Register the new reference file in manifest.json so it’s included in the skill bundle.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
skills/databricks-apps/SKILL.md	Adds a “Managing files in UC Volumes” pointer to the new Files guide.
skills/databricks-apps/references/appkit/files.md	New documentation page covering scaffolding, configuration, APIs, routes, and UI examples for the Files plugin.
manifest.json	Includes the new Files reference in the databricks-apps skill file list.

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[Copilot]

In the File Browser Example, Button and NewFolderInput are imported but never used. With this template’s noUnusedLocals setting, copy/pasting this snippet will fail to compile unless those imports are removed or the example demonstrates their usage.

Suggested change

	Button,
	DirectoryList,
	FileBreadcrumb,
	FilePreviewPanel,
	NewFolderInput,
	DirectoryList,
	FileBreadcrumb,
	FilePreviewPanel,

[Copilot]

setVolumeKey is declared but unused (const [volumeKey, setVolumeKey] = useState(...)). With noUnusedLocals, this will be a TypeScript error for anyone copying the snippet; either remove the setter or add UI showing how to switch volumes.

[Copilot]

loadDirectory assumes the response is always a DirectoryEntry[] and immediately calls res.json() + data.sort(...). Since the docs state errors return { error, plugin }, a non-2xx response will break at runtime; please check res.ok and surface data.error (or throw) before sorting.

[Copilot]

The preview fetch path doesn’t check response.ok before parsing JSON and calling setPreview. On error responses ({ error, plugin }), this will set an invalid shape into preview and likely break rendering; handle non-2xx explicitly (similar to the upload/delete patterns below).

Suggested change

	.then((r) => r.json())
	.then(setPreview);
	.then(async (r) => {
	if (!r.ok) {
	// Handle non-2xx responses without updating preview state
	const errBody = await r.json().catch(() => null);
	console.error('Failed to load file preview', errBody ?? r.statusText);
	return null;
	}
	return r.json();
	})
	.then((data) => {
	if (data) {
	setPreview(data);
	}
	});

[Copilot]

Using window.open(..., '_blank') without noopener/noreferrer can enable reverse-tabnabbing. Consider adding noopener,noreferrer (or using an <a target="_blank" rel="noopener noreferrer"> pattern) in the example.

Suggested change

	window.open(apiUrl('download', { path }), '_blank')
	window.open(apiUrl('download', { path }), '_blank', 'noopener,noreferrer')